An assay for allopurinol and its metabolite oxipurinol has been developed which is sensitive to 0.1 micro M concentration of either drug. Using this assay system, we will investigate the binding of allopurinol and oxipurinol to xanthine oxidase in terms of binding sites per molecule of xanthine oxidase, pH optimal for binding, and reduction state of xanthine oxidase needed for optimal binding. Clinical studies will attempt to correlate serum cereatinine levels with serum allopurinol levels in patients with renal failure to determine dose adjustments for renal failure in order to minimize toxicity. The effects of hemodialysis on allupurinol clearance will also be measured. The effect of allopurinol on the urinary excretion of xanthine, hypoxanthine and uric acid in patients undergoing treatment of malignant disease will be investigated. Patients with lymphomas, leukemias, testicular cancer and small cell lung cancer will be studied to measure rates of various purine excretion before and after chemotherapy for their malignancy.